Without caring about the d6-pawn.
18. a1d1  18... d4g7  19. f2f3 White's pawns have lost some of their mobility, but the rest of the advantage is maintained: more space and the possibility of attacking on d6. White should still be alert to always have the option of responding to a5-a4 with b3-b4. 19... c8c7  20. c2d2 